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Subject: Re: Best strategy for adding new nodes to the cluster
From: Janne Jalkanen <janne.jalkanen@ecyrd.com>
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Date: Tue, 28 Sep 2010 12:19:16 +0300
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On 28 Sep 2010, at 08:37, Michael D=FCrgner wrote:

>> What do you mean by "running live"? I am also planning to use =
cassandra on EC2 using small nodes. Small nodes have 1/4 cpu of the =
large ones, 1/4 cost, but I/O is more than 1/4 (amazon does not give =
explicit I/O numbers...), so I think 4 small instances should perform =
better than 1 large one (and the cost is the same), am I wrong?
>=20
> Based on results we saw and what you also find in different sources =
around the web, EC2 small instances perform worse than 1/4 regarding IO =
performance.

Ditto. My tests indicate that while the peak IO performance of small =
nodes can be ok (up to 1/2 of large), it degrades over time down to 1/6 =
or even less. It seems that Amazon dedicates sufficient bandwidth to =
small nodes in the beginning to ensure a smooth and quick boot, but then =
throttles down fairly aggressively within a few minutes.  This seems to =
affect reads more than writes, though.

Note also that large instances have over 4x the memory (1.7 GB =3D> 7.5 =
GB), and that makes a world of difference (you can have larger caches, =
for example). You don't really want to start swapping on the small =
instances.

(However, small instances are awesome for doing testing and learning how =
to manage a cluster.)

/Janne=